Today, there is an increased need for invasive measurements of physiological variables. For example, when investigating cardiovascular diseases, it is strongly desired to obtain local measurements of blood pressure and flow in order to evaluate the condition of the subject under measurement. Therefore, methods and devices have been developed for disposing a miniature sensor inside the body of an individual at a location where the measurements should be performed, and for communicating with the miniature sensor. Typically, the miniature sensor is arranged at a distal end of a guide wire, which is generally known in the art, and used for example in connection with treatment of coronary disease. The distal end of the guide wire is inserted into the body of a patient, for example into an opening into the femoral artery, and placed at a desired location. Once the guide wire is placed by the physician into the appropriate location, the miniature sensor can measure the blood pressure and/or flow. Measurement of blood pressure is a way to diagnose e.g. the significance of a stenosis. Further, a catheter of appropriate type may be guided onto the guide wire. Balloon dilation may then be performed. When measuring distal blood pressure (Pd), the sensor must be inserted into a vessel distal of the stenosis. For evident reasons, the dimensions of the sensor and the guide wire are fairly small; the guide wire typically has a diameter of 0.35 mm.
When diagnosing the significance of a stenosis in a hospital or a clinic, a catheter in connection with a first sensor is inserted into a patient proximal to a potential stenosis (typically visualized by means of flouroscopy). The sensor is connected to a central monitoring device via electrical leads. The central monitoring device used to monitor the patient's vital status, including blood pressure measured via the first sensor, is referred to as a cathlab monitor. In case of a stenosis, the vessel is narrower than normal, which impedes the flow of blood at the stenosis. When a narrowing of a vessel is seen on an angiogram, it is recommended that Fractional Flow Reserve (FFR) should be measured to determine the extent of the blood pressure difference proximal and distally of the stenosis.
FFR is approximated as Pd/Pa. The FFR is a measure of the pressure distal to a stenosis relative to the pressure proximal to the stenosis. Thus, FFR expresses vessel blood flow in the presence of a stenosis compared to the vessel blood flow in the hypothetical absence of the stenosis. Other physiological parameters may further be measured and transferred to the cathlab monitor. Should the FFR measurement show that there is a large drop in pressure in the vessel, treatment of the patient is required, for example by means of opening the vessel up with a balloon or stent, or by surgery for a coronary artery bypass.
To measure the distal blood pressure, the aortic blood pressure sensor is in prior art disconnected from the patient and the cathlab monitor. Then, a second sensor is used (which was discussed in the above) to measure Pd. This second sensor is inserted into the patient distal of the potential stenosis. The second sensor and the first sensor are connected to a small and easy-to-use monitoring device offering additional functionality. Thus, as can be seen in FIG. 3, pressure signals are connected to the smaller monitoring device 304 which in turn relays the pressure signals to the cathlab monitor 305.
This approach has drawbacks. For instance, connecting the smaller monitoring device to an up-and-running system requires disconnection of connectors carrying pressure signals to the cathlab monitor and reconnection of these connectors to the cathlab monitor via the smaller monitor. Further, in addition to the obviously tedious manual disconnecting operation, the disconnection of pressure signal connectors implies recalibrating the monitors, which is an undesired procedure.